1. Field of the Invention
The invention relates to an amplifier device; a method for operating an amplifier device; and to electronic devices including an amplifier device.
2. Related Art and Other Considerations
In amplifier devices control of the gain of an amplifier may be required. For example in integrated receivers used for the reception of radio signals it may be necessary to control the gain if a very large (adjacent) channel interference is present in the frequency spectrum of the received signals.
It is known in the art to control the gain of an amplifier device in an analog way by changing the gain determining elements in the amplifier device. For example, if the gain is controlled by a resistance, a second resistance may be placed in series or in parallel, thus increasing or reducing the gain.
It is also known in the art to control the gain of an amplifier device with a differential pair, for instance, two bipolar transistors with their emitters connected to each other and the collectors forming differential output contacts. The desired attenuated signal is then obtained from one of the differential output contacts while the other differential output contact is disregarded.
Furthermore, it is known to control the gain of an amplifier device by adjusting the DC bias current of the amplifier device. This may for example be implemented with a bipolar junction transistor (BJT) connected with the collector to an adjustable current source. The bias current is then controlled by the voltage over the base of the BJT.
However, each of the known gain controls is disadvantageous because of one or more of the following reasons. The control curve (i.e. the attenuation as a function of control signal) may be non-linear; the implementation or design of the device is complicated and time-consuming; or the generation of the control voltage has to be implemented in an analog (not digital) way.